Table 1.
Autoantibodies in myositis, their target antigens, M.W., frequency, and clinical significance.
| Antibodies | Nature of target antigens | MW of antigens in kDa | Frequency In IIM (%) | Clinical significance |
|---|---|---|---|---|
| MYOSITIS-SPECIFIC AUTOANTIBODIES (MSAs) | ||||
| anti-ARS | ||||
| anti-Jo-1 | Histidyl-tRNA synthetase | 50/52 | 15–20 | Antisynthetase syndrome (myositis, interstitial lung disease, polyarthritis, mechanic’s hand Raynaud’s phenomenon, fever) |
| anti-PL-7 | Threonyl-tRNA synthetase | 83 | 5–10 | |
| anti-PL-12 | Alanyl-tRNA synthetase | 70 | <5 | |
| anti-EJ | Glycyl-tRNA synthetase | 75 | 5–10 | |
| anti-OJ | Isoleucyl-tRNA synthetase | 145 | <5 | |
| anti-KS | Asparaginyl-tRNA synthetase | 63 | <5 | |
| anti-Zo | Phenylalanyl-tRNA synthetase | 52 | <1 | |
| anti-YRS | Tyrosyl-tRNA synthetase | 59 | <1 | |
| anti-SRP | Signal recognition particle | 9–72 | <4 | Necrotizing myopathy |
| anti-Mi-2 | Mi-2α/Mi-2β helicase family proteins | 240/218 | 5–10 | Dermatomyositis |
| anti-CADM-140 | Melanoma differentiation-associated gene 5 (MDA-5) | 140 | 50 (C-ADM) | Specific in C-ADM and acute ILD |
| Anti-p155(/p140) | Transcriptional intermediary factor 1γ (TIF1-γ) | 155/140 | 20 (DM) | Dermatomyositis, especially in cancer-associated dermatomyositis |
| anti-MJ | Nuclear matrix protein (NXP-2) | 140 | <23 | Juvenile dermatomyositis |
| anti-PMS1 | DNA repair mismatch enzyme | 120 | 7.5 | DM and PM |
| anti-SAE | Small ubiquitin-like modifier activating enzyme | 40/90 | <4 | Dermatomyositis |
| anti-HMGCR | HMG-CoA reductase | 200/100 | 62% | Statin-induced autoimmune-necrotizing myopathy |
| MYOSITIS-ASSOCIATED AUTOANTIBODIES (MAAs) | ||||
| anti-U1RNP | U1 small nuclear RNP | 11–70 | 10 | Overlap myositis, MCTD |
| anti-SS-A/Ro | Ro-52/TRIM21 and Ro-60 proteins | 52/60 | ≥35% | ILD in IIM patients |
| anti-Ku | DNA-PK regulatory subunit | 70/80 | 20–30 | Polymyositis–SSc overlap in Japanese |
| anti-PM-Scl | Nucleolar protein complex of 11–16 proteins | 75/100 | 10–15 | Polymyositis–SSc overlap |
ARS, aminoacyl-tRNA synthetases; C-ADM, clinically amyopathic dermatomyositis; ILD, interstitial lung disease; HMGCR, 3-hydroxy-3 methylglutaryl-coenzyme A reductase; DNA-PK, DNA-dependent protein kinase; MCTD, mixed connective tissue disease; SSc-scleroderma. MW, molecular weight; kDa, kilodalton.